I would like to know what is the minimal biological interdependent function that has been identified in evolutionary terms.

When I mean function, I mean:a) something that biologists feel evolved after the initial cell/self-replication was in placeb) was absent at one point in timec) is not simply a reversible variation (adaptable feature)d) a concrete mechanism at the molecular levele) when I mean "interdependent", this just means a natural outcome of the mechanism that was "added" which is now dependent and dependent upon by other functionality within the system.

I'm sorry if my question is framed inappropriately as I am not a biologist of any type.

I would really appreciate the feedback and links and references to papers if possible.